Pressure transducer structures suitable for curved surfaces

ABSTRACT

A novel flexible transducer structure is suitable for attaching to curved surface such as the leading edge of an aircraft wing. The structure comprises a thin flexible sheet of an insulating material with a leadless transducer secured to the sheet. The sheet is then placed over the curved surface and assumes the curvature of the surface. The transducer secured to the sheet provides an output of pressure according the pressure exerted on the sheet. The sheet basically is fabricated from a thin material such as Kapton and is flexible so as to assume the curvature of the surface with the transducer being exposed to pressure applied to the curved surface. The sensor in conjunction with the flexible sheet allows pressure to be measured without disturbing the air flow patterns of the measuring surfaces and because of its construction, is moisture resistant over a large variety of atmospheric conditions.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application claiming priority to co-pending U.S.patent application Ser. No. 12/291,870, filed on Nov. 14, 2008, which ishereby incorporated by reference in its entirety as if fully set forthherein.

FIELD OF THE INVENTION

This invention relates to pressure transducers and more particularly toa flexible transducer structure suitable for non-intrusively attachingto a curved surface.

BACKGROUND OF THE INVENTION

As one can ascertain, semiconductor pressure transducers are widely usedin many applications. Certain of these applications involve placing atransducer on a surface which is curved. Such a surface, for example,may be the leading edge of an aircraft wing or the front of anautomobile or vehicle. Such tests may be performed in wind tunnelswhereby the effects of airflow past the object can be determined. In anyevent, by placing the pressure transducer on the object which is heldstill in moving air, one can obtain pressure measurements in an easy andsimple manner. As one can ascertain, pressure transducers in the priorart are while mounted on curved surfaces, would adversely affectairflow, as will be further explained. It is an object of the presentinvention to provide a pressure transducer which is flexible and whichcan be attached to a curved surface of an aircraft wing or some othercurved surface while providing minimal disturbance to air flow patterns,as for example, as measured in a wind tunnel or some other environment.As will be explained, the structure is thin and flexible enough so thatit can be easily attached to a variety of bent/contoured surfaceswithout disturbing the airflow patterns above these measuring surfaces.As will be further explained, because of the construction the transduceris moisture resistant over a wide variety of atmospheric conditions. Asone will ascertain, the assignee herein, namely Kulite SemiconductorInc., has provided many transducers which have been utilized in allsorts of environments. The applicant herein particularly has provided aultra thin piezoresistive leadless sensor. These sensors are made ofsilicon and have been widely employed. For example of such devices,reference is made to U.S. Pat. No. 5,955,771 entitled Sensors for Use inHigh-Vibrational Applications and Methods for Fabricating the Same to A.D. Kurtz, et al. and issued on Sep. 21, 1999. Reference is also made toU.S. Pat. No. 5,973,590 entitled Ultra Thin Surface Mount Wafer SensorStructures and Methods for Fabricating the Same issued on Oct. 26, 1999to A D. Kurtz, et al. and assigned to Kulite Semiconductor Products Inc,the assignee herein. Both patents are incorporated herein in theirentirety. As will be explained, the leadless device as indicated anddescribed in both patents, is employed together with a flexible circuitto be described which will enable one to have a flexible transducerstructure suitable for mounting to a curved surface and withoutdisturbing airflow patterns.

SUMMARY OF THE INVENTION

A pressure transducer, comprising a thin flexible insulator sheet havinga top and bottom surface, and having a plurality of metal tracesemanating from a first location on said sheet to a second location, saidtraces arranged to accommodate contact terminals at said first location,a leadless sensor having contacts configured to be accommodated by saidtraces whereby said sensor is positioned on said sheet at said firstlocation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a bottom view of a leadless sensor employed in thisinvention.

FIG. 1B is a cross-sectional view of a leadless sensor of FIG. 1A.

FIG. 1C is a top view of the leadless sensor.

FIG. 2A is a top view of the leadless sensor secured to a thin flexibleinsulating sheet such as Kapton according to this invention.

FIG. 2B is a bottom view of the sensor shown in FIG. 2A.

FIG. 2C is sectional view taken through line A-A of FIG. 2B.

FIG. 2D is an enlarged cross sectional view showing the sensor securedto a thin plastic flexible layer.

FIG. 3A is a top view showing a sensor mounted to a curved surface.

FIG. 3B is a cross sectional view of FIG. 3A showing the sensor mountedto a air foil and positioned in a recess.

FIG. 4A is a top view depicting another configuration of the sensorwhile FIG. 4B is a cross sectional view showing the sensor mounted on anair foil without a recess.

FIG. 5A is a top view of the sensor while FIG. 5B is cross sectionalview showing a sensor together with a cover member.

FIG. 6 is an enlarged view of the sensor configuration depicted in FIG.5B.

FIG. 7 is a cross sectional view of an alternate embodiment of a sensormounted in a recess.

FIG. 8 is a cross sectional view showing the sensor mounted directly onthe curved surface.

FIG. 9 is a cross sectional view showing a sensor mounted on a flexiblecircuit.

FIG. 10 is an enlarged view depicting an alternate type of sensor inconjunction with a flexible circuit.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, as one can ascertain, FIG. 1 consists of 1A, 1B and1C. FIG. 1A is a bottom view of a leadless sensor according to theteachings of this invention. FIG. 1B is a side cross-sectional view ofthe sensor of FIG. 1A. FIG. 1C is a top-view of the sensor depicted inFIGS. 1A and 1B. In any event, the sensor as shown FIG. 1 is well knownand is basically supplied by the assignee herein and designated as aleadless device. As one can ascertain from FIG. 1B, the sensor containsa central layer or substrate of silicon 20 which is processed to includepiezoresistors, the silicon layer 20, as indicated has piezoresistors as30 formed within active areas as designated by numerals 26 and 27. Theactive areas are thin and constitute diaphragm areas which will deflectupon application of a force via the port 25. As seen, the silicon layer20 has bonded thereto a glass cover wafer 28, which glass cover waferenables one to provide a hermetic seal. Bonded to the other side of thesilicon layer 20 is a contact glass wafer or layer 29. The contact glasslayer has apertures such as 23 and 24 which communicate with contacts onthe silicon layer 20. The apertures as 23 and 24 are filled with aconductive glass frit to enable contacts to be made with thepiezoresistive sensors or Wheatstone bridge configurations formed on thesemiconductor layer 20. As seen in FIG. 1A, the contacts, as forexample, 23 and 24 are brought to the bottom surface which has thepressure port 25 located therein. As seen from FIG. 1C, the sensorconfiguration is shown with FIG. 1C in the top view with the dash linesindicating the active area of the silicon chip 20. While the sensor hasa cover and pressure is applied via port 25, it is well known that thereare many other configurations for such sensors. In any event, in regardto the above-noted description of FIG. 1 reference is again made to U.S.Pat. No. 5,973,590 and particular reference is made to FIGS. 6 and 7which shows such a configuration. It is of course again indicated thatthe above noted patent describes in detail the structure as well as themethods of forming the same. And as indicated above, the entire Patentis incorporated herein by reference. Reference is also made to theabove-noted U.S. Pat. No. 5,955,771 which is also incorporated herein inits entirety. That patent shows various configurations employed withsensors as shown in FIG. 1 including the sensor mounted in a suitableheader as its normal use. As will be understood herein, the sensordepicted in FIG. 1 is not mounted in the header but is, as seen, will bemounted in conjunction with the flex circuit configuration. As depictedherein, the leadless chip shown in FIG. 1 basically depicts an absolutechip but is also known that other sensors can be employed with thisinvention as well, such as differential sensors and so on. All theseconfigurations are known in the art. The absolute sensor, depicted inFIG. 1, is less than a millimeter in thickness and approximately severalmillimeters in length and width. Thus, as seen, the chip is extremelysmall.

As seen in FIG. 2A, the leadless sensor 40 which is for example, asensor depicted in FIG. 1, is placed at the center of a thin Kaptonsheet or Kapton flex sheet 41. The Kapton flex sheet has deposited orformed thereon metalized traces or metalized contacts paths as 42 and43. These contacts or paths are formed by typical printed circuittechniques as by photolithography or other well known techniques. Thecontacts from the semiconductor sensor 40, as for example shown in FIG.1 are placed on suitable contact areas associated with the Kapton flexcircuit or sheet 41. There can also be additional components depositedthereon such as span resistor 45 and so on. As seen, the Kapton flexcircuit or sheet also has vent hole 46. Thus the semiconductor sensor 40is placed on the Kapton sheet as shown in FIG. 2A. In FIG. 2B there isshown a bottom view of the Kapton sheet 41. The bottom view is called41B as compared to the top view as shown in FIG. 2A which is 41P. Asseen from the bottom view, there is the thin sheet of Kapton which hasthe vent hole 46 and has a pressure inlet port 47. The inlet portcommunicates directly with the semiconductor sensor and essentially isequivalent to port 25 shown in FIG. 1. Thus the sensor can receive apressure at the inlet port. Referring to FIG. 2C there is shown across-sectional view taken through line A-A of FIG. 2B. Thus in FIG. 2C,one can see the sensor is mounted directly on the thin Kapton sheet 41which has a bottom surface 41B and a top surface 41T. The sensor 40communicates with the pressure inlet aperture 47. The vent hole isapproximately 0.02 inches in diameter while the Kapton sheet is 0.002inches thick. Thus as indicated, this is extremely small. As one cansee, the configuration of FIG. 2B basically shows a rectangular topsheet area 51 which is co-extensive with a trace section 50. The topsection 51 is a square configuration but can be of any other geometricconfiguration. Referring to FIG. 2D there is shown an enlarged view ofthe vent hole 46, the pressure inlet port 47 and the leadless sensor 40.Thus one can really ascertain from FIG. 2D how the sensor is mounted tothe Kapton sheet. The sensor can be mounted to the Kapton sheet by meansof any type of bond including an epoxy, glue or some other convenientbond and therefore makes for easy mounting of the sensor on the flexibleand thin Kapton sheet. There can be a second layer or sheet of Kapton 48secured to layer or sheet 41. The sheets 41 and 48 sandwich theconductive traces between them and therefore protect them. However, onlya single sheet 41 can be used with the traces coated with an insulatedlayer with an insulating layer such as a plastic, varnish and so on.

Referring to FIG. 3, there is shown a FIG. 3A a top view of the flexibletransducer mounted on an air foil 57. The air foil 57 is a curvedsurface. As seen in FIG. 3A there is shown the vent hole 46, thepressure port 47 as well as the top section of the flexible transducer50 and the bottom handle section 51. Wires such as 53 and 54 areconnected to the copper or metalized traces such as traces 42 and 43 ofFIG. 2A. The wires are brought out to suitable monitoring circuit. Seenin FIG. 3B is the curved surface of the air foil 57. The air foil 57 hasa cavity or recess depicted therein or a recess 56. The semiconductorsensor 40 sits into this recess 56 and hence the flexible circuit, whensecured or mounted to the air foil by means of a suitable epoxy or othertype bond, has the same exact contour as the air foil while the pressuresensor 40 mounted in the recess does not in any manner effect the shapeof the air foil. So as indicated, the structure depicted is capable ofbeing bent around a leading edge of wing or air foil with a radius ofcurvature of 10 or more inches and the structure makes it moistureresistant. In a typical mounting installation, the recess 56 isintroduced into the measurement surface enabling the transducer 40 to beflush mounted. The recess 56 is large enough to accept the sensingelement. In this way, as depicted in FIG. 3B, there is substantially noflow disturbance provided by the transducer during typical measurement.It is also obvious, that it is part of such flush mount installation,the cavity can be eliminated and a flexible transducer can be mounteddirectly on the installation surface.

Referring to FIG. 4 where the same reference numerals have been used todepict the air foil 57 and the flexible transducer having a top section50 and a bottom section 51. As one can see in FIG. 4B, the device now ismounted directly on the curved surface of the air foil 57. The flexibletransducer structure bends at this area, but the pressure port 47directly communicates with the sensor 40 as well as the vent hole. Theleads from the flexible circuit 53 and 54 are then directed out asconnected to the metal traces of the flexible circuit. As seen in FIG.4, this approach significantly simplifies the installation process whileextending the flexible circuit by only a few tenths of mils into the airflow. By eliminating the cavity, the mounting surfaces will not need tobe machined or prepped in any way, thus avoiding any possible damage tothese measurements.

Referring to FIG. 5, there is shown the same view of the sensor in FIG.5A with the cover member 60 enclosing the sensor 40. In this manner, thecover member protects the sensor chip during installation by insuringthat the chip is covered and kept apart from any glue or epoxy lines.The cover 60 also acts to seal off the back of the sensor and of theentire mounting area from the pressure media. A pressure inlet hole isintroduced in the flex circuit to enable application of pressure to thesensor. A vent hole, as shown in FIG. 5A is also again used to enablethe venting of any potential cavity formed around the cover duringinstallation. The vent hole is located next to the sensing chip and isoutside the footprint of the cover as shown, for example, in FIG. 5Bwhere vent hole 46 is outside the cover with pressure port 47communicating with the cover.

Reference is made to FIG. 6 this is more clearly shown where the venthole 46 is outside the cover 60 with the cover 60 enclosing thesemiconductor chip 40 and with the semiconductor chip communicating withthe pressure inlet port 47. It is also known that while the Kapton layeris extremely thin, as for example 0.002 inches thick, it can bestiffened by a adding a nickel plated copper layer on top of the Kaptonlayer, that this will enable the flexible circuit to act more like apiece of foil rather than a thin plastic film. In any event, it is up tothe user to select which type of Kapton he wishes to use. In any event,in using the sensor shown in FIGS. 5 and 6, one can again mount thedevice to the air foil 47, as shown in FIG. 7.

In FIG. 7 there is a recessed cavity in the air foil, namely cavity 65.The sensor is mounted within the cavity 65 where the sensor and itscover is shown mounted to the air foil.

FIG. 8 of course shows the transducer and its cover mounted directly tothe air foil 57 without the use of a recess in the air foil.

As shown in FIG. 9, the modified flexible circuit is shown. In FIG. 9the sensor chip 40 is fabricated without a hole in the contact glass andwill have a hole in the cover glass for enabling pressure application tothe micromachined side. This sensing chip is mounted to the flex circuitwhich again consists of formed copper conductors which may be sandwichedbetween two films of Kapton, and the holes in the upper Kapton layerpermit contacts to be made with the reverse side of the chip. As statedprior, such a structure is capable of being bent around a leading edgeof a wing as shown in FIG. 9, with a radius of curvature of ten inchesand the makeup of its structure enables it to be moisture resistant. Asone can see from FIG. 9, the leadless chip 40 is mounted directly on thetop surface of the flexible Kapton member. The chip, as depicted forexample in FIG. 1 will have an aperture in the glass cover member 28while the contact glass will not have an aperture, thus pressure wouldbe applied to the bottom side of the chip via the bottom aperture.

Referring to FIG. 10 there is shown a chip such as FIG. 1B but where thecontact glass member 74 has no aperture with an aperture 73 in the coverglass member for communicating with the underside of the chip. There isa pressure inlet port 75 and a vent hole 76. There is shown a covermember 72 which covers the chip and a thin Kapton layer 71 to which thecover member and the chip are glued or secured to. The pressure inlethole 75 introduced in the flex circuit enables the application ofpressure into the cavity formed around the sensor chip by the cover.This inlet hole is located next to the sensing chip and within thefootprint of the cover. In this construction, the applied pressure actson the sensor chip in the exact same manner as in a typical leadlessconstruction described above and shown in the above noted patents U.S.Pat. No. 5,955,771 and U.S. Pat. No. 5,973,590. A vent hole 76 isintroduced in the flex circuit to enable the venting of any potentialcavity formed around the cover during the installation. The vent hole 76is located next to the sensing chip and is outside the footprint of thecover. In using such flexible transducer with a cover, the mountingsurface can either be prepared with a cavity to accept the cover, asdescribed above, or the cavity can be eliminating and the flextransducer can be directly mounted, as for example depicted above inregard to other transducers. It is thus seen that the above notedstructure enables one to utilize ultra thin transducers of the leadlesstype in regard to flexible circuitry which will enable accuratemeasurements to be made without basically disturbing air flow. It willbe apparent to those skilled in the art that there are many alternateembodiments which can be depicted using the techniques described aboveand all such alternate embodiments are deemed to be encompassed withinthe spirit and scope of the invention depicted herein.

1. A pressure transducer assembly, comprising: a flexible sheet having afirst layer; a plurality of conductive traces disposed on the firstlayer of the flexible sheet, extending from a first location on theflexible sheet to a second location on the flexible sheet; and a sensorattached to the flexible sheet and in electrical communication with theplurality of conductive traces, wherein the sensor is adapted to measurean incoming air pressure directly applied to the sensor.
 2. The pressuretransducer assembly of claim 1, further comprising a pressure inlet portdefined through the flexible sheet and aligned with the sensor, whereinthe pressure inlet port receives the incoming air pressure and directlyapplies the incoming air pressure to the sensor.
 3. The pressuretransducer assembly of claim 1, further comprising a vent hole definedwithin the flexible sheet.
 4. The pressure transducer assembly of claim3, wherein the vent hole is about 0.02 inches in diameter.
 5. Thepressure transducer assembly of claim 1, wherein the flexible sheet isfabricated from a Kapton material.
 6. The pressure transducer assemblyof claim 1, wherein the flexible sheet is about 0.002 inches inthickness.
 7. The pressure transducer assembly of claim 1, wherein theconductive traces are copper conductors.
 8. The pressure transducerassembly of claim 1, wherein the conductive traces are coated with aninsulating layer.
 9. The pressure transducer assembly of claim 1,wherein the sensor is a silicon piezoresistive sensor.
 10. The pressuretransducer assembly of claim 1, wherein the sensor is attached to theflexible sheet with epoxy, glue, or combinations thereof.
 11. Thepressure transducer assembly of claim 1, further comprising a covermember enclosing the sensor and adapted to shield the sensor fromexternal environments.
 12. The pressure transducer assembly of claim 1,further comprising a nickel plated copper layer deposited on the topsurface of the flexible sheet to stiffen the flexible sheet.
 13. Apressure transducer assembly, comprising: a flexible sheet having afirst layer and a second layer; a plurality of conductive tracesdisposed between the first and second layers, extending from a firstlocation to a second location; and a sensor attached to the flexiblesheet and in electrical communication with the plurality of conductivetraces, wherein the sensor is adapted to measure an incoming airpressure directly applied to the sensor.
 14. The pressure transducerassembly of claim 13, further comprising a pressure inlet port definedthrough the flexible sheet and aligned with the sensor, wherein thepressure inlet port receives the incoming air pressure and directlyapplies the incoming air pressure to the sensor.
 15. The pressuretransducer assembly of claim 13, further comprising a vent hole definedwithin the flexible sheet.
 16. The pressure transducer assembly of claim15, wherein the vent hole is about 0.02 inches in diameter.
 17. Thepressure transducer assembly of claim 13, wherein the flexible sheet isfabricated from a Kapton material.
 18. The pressure transducer assemblyof claim 13, wherein the flexible sheet is about 0.002 inches inthickness.
 19. The pressure transducer assembly of claim 13, wherein theconductive traces are copper conductors.
 20. The pressure transducerassembly of claim 13, wherein the conductive traces are coated with aninsulating layer.